The bowline is the king of sailing knots. It has been in use by sailors continuously for at least 500 years. Simply put, the bowline is way of turning the end of your line into a loop. Why is this useful? You can tie it around a post or other fixed object to make the line fast, or on smaller boats it is used fasten the halyard to the sail. It can also be used to tie two lines together. It has a number of practical uses as well, such as hanging a hammock. Under pressure the bowline tightens, so it won’t give way. However, note that it’s impossible to untie while bearing a large load.